Motor still noisy with shielded cable
Close
Login to Your Account
Results 1 to 4 of 4
  1. #1
    Join Date
    Jul 2018
    Country
    AUSTRALIA
    Posts
    1
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default Motor still noisy with shielded cable

    I have a poorer quality single phase VFD providing power to a 3 phase motor (both 240v), yesterday I fitted shielded cable and it obviously runs quieter but at the motor (not at the VFD 3 meters away) it still makes a high pitched whine. I followed a Beldon VFD wiring best practice guide and grounded the ground and shield together at both ends, VFD and motor.

    Is the motor just noisy? I would love to know how to make it any quieter if it's possible. It's bolted onto a metal frame (which its grounded to with 2 other motors), but only testing 1 motor at the moment. It's wired in Delta. I have attached the motor data plate.
    Attached Thumbnails Attached Thumbnails plate.jpg  

  2. #2
    Join Date
    Dec 2008
    Location
    Vt USA
    Posts
    6,092
    Post Thanks / Like
    Likes (Given)
    567
    Likes (Received)
    1907

    Default

    Quote Originally Posted by user322 View Post
    I have a poorer quality single phase VFD providing power to a 3 phase motor (both 240v), yesterday I fitted shielded cable and it obviously runs quieter but at the motor (not at the VFD 3 meters away) it still makes a high pitched whine. I followed a Beldon VFD wiring best practice guide and grounded the ground and shield together at both ends, VFD and motor.

    Is the motor just noisy? I would love to know how to make it any quieter if it's possible. It's bolted onto a metal frame (which its grounded to with 2 other motors), but only testing 1 motor at the moment. It's wired in Delta. I have attached the motor data plate.
    Shielded cable on a 10 foot run should not be needed.

    Just what got "shielded" or shunted to ground that would make the motor growl?

    Suppressing resonance and impedance mismatch is a good thing, but over 3 meters, I'm not sure of the improvement potential.

    Play around with carrier frequency to see if things can be less trouble. Then play with actual applied power frequency to the motor.
    There are "frequency skip" settings on many VFDs just to get over and around the sore spots.

  3. #3
    Join Date
    Jun 2001
    Location
    St Louis
    Posts
    17,007
    Post Thanks / Like
    Likes (Given)
    1493
    Likes (Received)
    2655

    Default

    Not very likely that the acoustic noise is much affected by shielding. Radio emission, sure, and you did just right by grounding both ends, providing a low impedance return path.

    Frequency, use of an inductor on the VFD output, those may help.

    Much of the noise will relate to waveshape, and carrier frequency. Move that up and the noise should be reduced, but you will also get more heating of the VFD.

    Noise is also worse on the chinese motors, because they often do not dip the windings in varnish, nor even tie them. Many things can vibrate, and if not held by varnish, they all will vibrate. It;s a known thing, even the chinese admit that many of their motors are not very good.

  4. #4
    Join Date
    Aug 2004
    Location
    San Ramon, CA USA
    Posts
    2,545
    Post Thanks / Like
    Likes (Given)
    23
    Likes (Received)
    542

    Default

    Shielded cable helps with ELECTRICAL noise issues, not AUDIBLE noise issues. Audible noise in the motor is related to the "carrier frequency" of the DC pulses coming out of the VFD, working on the "magnetostrictive" qualities of the laminated steel used in the stator frame of the motor. As mentioned, cheaper motors don't bother with taking steps to minimize this, but it can happen even in the best motors depending on circumstances.

    In most VFDs, you can adjust that Carrier Frequency (sometimes called the PWM Frequency") value, which raises the audible noise frequency so at about 10kHz and above, most humans can no longer hear it (but it will drive your dog nuts). Raising the carrier frequency however also increases the rate at which the transistors fire, which then raises the amount of "switching losses" inside of the VFD itself, so often it means de-rating the VFD. You must check with the VFD manufacturer for how much de-rating is required.


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
2